40011108 Mercury SCREW

Pistons, Rings, and Connecting Rods
One-piece aluminum pistons are used in most applications. Engines with higher cylinder pressures require two-piece pistons. Refer to the parts manual in order to obtain information about the type of piston that is used in a specific engine.The one-piece aluminum pistons have an iron band for the top two rings. This helps to reduce wear on the compression ring grooves. Oil from the piston cooling jets will spray the underside of the piston. This will cool the piston, which improves the life of the piston and rings. The piston has two compression rings and one oil ring. All of the rings are located above the piston pin bore. The oil ring is of the standard or conventional type. Oil will return to the crankcase through holes that are located in the groove for the oil ring. The design of the compression rings is of the keystone type, which is tapered. The piston groove is also tapered. Too much carbon deposits can cause seizure of the piston rings. This is prevented by the action of the rings in the piston grooves.The two-piece piston consists of an alloy steel crown that is connected to an aluminum skirt by the piston pin. Oil from the piston cooling jets will spray the underside of the piston crown. This will cool the piston, which improves the life of the piston and the rings. The piston rings are located in grooves in the piston crown. Oil will return to the crankcase through holes that are located in the groove for the oil ring.The connecting rod has a taper on the pin bore end which gives the rod and the piston more strength in the areas with the most load. The cap is fastened to the connecting rod by two bolts. This design keeps the rod width to a minimum, so that the piston can be removed through the cylinder.Crankshaft
The crankshaft converts the combustion forces in the cylinders into rotating torque which powers the equipment. A vibration damper is used on the front of the crankshaft to reduce torsional vibrations (twist on the crankshaft) that can cause damage to the engine. The crankshaft drives a group of gears (front gear train) on the front of the engine. The front gear train provides power for the following components:
Engine oil pump
Camshaft
Governor
Air compressor
Power steering pumpIn addition, the front belt pulleys on the crankshaft provide power for following components:
Radiator fan
Water pump
Alternator
Refrigerant compressorHydrodynamic seals are used at both ends of the crankshaft to control oil leakage. The hydrodynamic grooves in the seal lip move lubrication oil back into the crankcase as the crankshaft turns. The front seal is located in the front housing. The rear seal is installed in the flywheel housing.
Illustration 1 g00698014
Schematic of Oil Passages in a 4 Cylinder Engine (1) Oil gallery (2) Main bearings (3) Connecting rod bearings
Illustration 2 g00698015
Schematic of Oil Passages in a 6 Cylinder Engine (1) Oil gallery (2) Main bearings (3) Connecting rod bearingsPressurized oil is supplied to all main bearings through drilled holes in the webs of the cylinder block. The oil then flows through drilled holes in the crankshaft in order to provide oil to the connecting rod bearings. The crankshaft is held in position by either five main bearings on the four cylinder engine or seven main bearings on the six cylinder engines. A thrust main bearing is located next to the rear main bearing. This type of main bearing is used in order to control the end play of the crankshaft. Camshaft
The camshaft is located in the upper left side of the cylinder block. The camshaft is driven by an idler gear that is turned by the crankshaft in the front gear train. Five camshaft bearings support the camshaft in a four cylinder engine. Seven camshaft bearings support the camshaft in a six cylinder engine. Each bearing journal is lubricated from the oil manifold in the cylinder block. A thrust pin that is located at the rear of the block positions the camshaft through a circumferential groove. The groove is machined at the rear of the camshaft.The camshaft has three lobes at each cylinder that operate the unit injector, the exhaust valves, and the inlet valves. As the camshaft rotates, each lobe moves a lifter assembly. Each outside lifter assembly moves a pushrod, which will move either an inlet valve or an exhaust valve. The center lifter assembly moves a pushrod that operates the fuel injector. The camshaft must be in time with the crankshaft. Timing is the relationship of the camshaft lobes to the crankshaft position, which will cause the valves and the fuel injector in each cylinder to operate at the correct time. Timing of the camshaft is accomplished by aligning marks on the following components with each other:crankshaft gear, idler gear and camshaft gear.Vibration Damper
The force from combustion in the cylinders will cause the crankshaft to twist. This is called torsional vibration. If the vibration is too great, the crankshaft will be damaged. The vibration damper limits the torsional vibrations to an acceptable amount in order to prevent damage to the crankshaft.Rubber Damper (If Equipped)
Illustration 3 g00698078
Cross Section of a Rubber Vibration Damper (1) Crankshaft (2) Ring (3) Rubber ring (4) Hub (5) Alignment marksThe rubber vibration damper is installed on the front of crankshaft (1). Hub (4) and ring (2) are isolated by a rubber ring (3). The vibration damper has alignment marks (5) on the hub and the ring. These marks give an indication of the condition of the vibration damper.Viscous Damper (If Equipped)
Illustration 4 g00698081
Cross Section of a Viscous Vibration Damper (1) Crankshaft (2) Weight (3) CaseThe viscous vibration damper is installed on the front of crankshaft (1). The vis